This article considers the provisions of the Mental Capacity Act 2005 in respect of advance decisions. It considers the new statutory regulation of advance directives (termed 'advance decisions' in the Act) and the formalities necessary to effect an advance decision purporting to refuse life-sustaining treatment. The validity and applicability of advance decisions is discussed with analogy to case law and the clinician's reasonable belief in following an advance decision is considered. The article assesses the new personal welfare Lasting Powers of Attorney, the situation where an attorney purports to refuse life-sustaining treatment on behalf of the donor, and the contrast between best interests and substituted judgment